Lyapunov hydrodynamics in the dilute limit

We study the hydrodynamic Lyapunov exponents of the hard-disk fluid in the dilute limit. These exponents appear in discrete groups and their values depend on the system size. In a previous paper [Phys. Rev. E 64 (2001) 051103], we presented a theory for these exponents, explaining them as the growth rate of collective, organized perturbations in phase space. That theory successfully described the basic features of the hydrodynamic exponents, but it had some difficulties. Many of these difficulties can be removed by considering the dilute limit.